Ariz. Const. art. 12, § 3

There are hereby created in and for each organized county of the state the following officers who shall be elected by the qualified electors thereof: a sheriff, a county attorney, a recorder, a treasurer, an assessor, a superintendent of schools and at least three supervisors, each of whom shall be elected and hold his office for a term of four (4) years beginning on the first of January next after his election, which number of supervisors is subject to increase by law. The supervisors shall be nominated and elected from districts as provided by law. The candidates for these offices elected in the general election of November 3, 1964 shall take office on the first day of January, 1965 and shall serve until the first day of January, 1969.